Absorption of carotenoids is a complex process involving release from the food microstructure matrix, dissolution into mixed micelles, intestinal uptake, incorporation into chylomicrons, distribution to the tissues, uptake by liver and re-secretion into VLDL, which are progressively transformed into LDL.
Lycopene absorption from food sources is widely documented. Lycopene bioavailability is quite low from foods such as tomatoes and tomato juice. Up to now, tomato paste is the best known food source for bioavailable lycopene. Tomato contains about >90% of lycopene in its all E configuration.
Tomato extracts containing a high amount of lycopene are commercially available in the form of oleoresin but the bioavailability of the lycopene in humans is rather limited from these sources. In concentrated tomato extracts, lycopene is mainly present in crystalline form, which has been suggested to be one of the primary factors that reduces its bioavailability.
To date, most commercially available lycopene sources display an isomeric profile quite similar to the starting tomatoes or show only a slight increase in Z-isomers, whether they are derivatives (such as sauces) or extracts. A number of treatments, as for instance thermal processing, are known to promote isomerization. Shi et al., Journal of Food Process Engineering 2003, 25, 485-498, showed that an increase in Z isomers could be obtained by heating tomato sauces. However certain lycopene isomers are not stable and prone to retro-isomerisation. According to the literature, 5-Z is the most stable among the predominant lycopene isomers followed by the all-E, the 9-Z and the 13-Z. Accordingly, the stability of isomerised lycopene based products depends on their lycopene isomer profile and thus can be modulated by technological processings affecting this profile.
Thermal isomerisation of lycopene is known to improve its bioavailability from food matrices. However, the bioavailability of individual lycopene isomers has not been investigated yet. As for stability, it can be assumed that bioavailability of lycopene based products is dependent on their lycopene isomer profile and thereby can be modulated by technological means.
There are already patents that propose technological means and formulations for improved bioavailibility of lycopene. For example, WO 2005/075575 provides a primary composition enriched in Z-isomers, effective to increase the bioavailability of lycopene.
EP 1 103 579 discloses a process for extracting lycopene by refluxing ethanol: the process is carried out for short time (30′) so that no significant isomerization occurs. Actually, the natural all-Z lycopene is desired as the final product.
WO 96/13178 discloses a process for the preparation of stable lycopene concentrates: the effect of isomerization on stability is not however appreciated and, on the contrary, the disclosed process tries to avoid isomerization by using temperatures lower than 50° C. for a few minutes, e.g. 10 minutes.
EP 1 201 762 refers to a lycopene-containing product wherein lycopene is in its natural all-trans form. No significant isomerisation takes place since any heat treatment (dissolution and concentration) is carried out for the shortest possible time (less than 1 hour).
KR 2005 006592 discloses the preparation of a lycopene-zinc complex having increased anti-oxidant activity. Hating is applied in the absence of solvents to break the cell walls of the plant material. No prolonged heating and no isomerization occurs.
WO 03/079816 discloses a process for the preparation of tomato extracts with high content in lycopene wherein the extraction is carried out at room temperature.
U.S. Pat. No. 5,837,311 and WO 97/48287 disclose a process for the preparation of an oleoresin having high content of lycopene and satisfactory stability. The latter feature is obtained by means of phospholipids and glycerides present in the oleoresin itself. No mention is made about the isomeric composition of lycopene and of its influence on the stability. An hot extraction is carried out in order to maximise the yield in lycopene but for times not longer than 1.2 hours. A heat pre-treatment is carried out on the tomatoes in the absence of any solvent only in order to improve the pulp-serum separation.
WO 2005/075575 addresses the problem of increasing the cis-isomers content in tomato oleoresins: isomerization is obtained, inter alia, by thermal treatment for short period of time. Moreover, the obtained product contains an high amount of the unstable 13-cis isomer.
EP 0 937 412 discloses a process for the preparation of finely divided pulverous carotenoid preparations including an heating step in the presence of solvents for very short times (5 seconds).
U.S. Pat. No. 5,858,700 concerns a process for the isolation and purification of lycopene crystals characterised by the hydrolysis of impurities such as glycerides and phosphonates. The hydrolysis is carried out at high temperature but for times shorter than 2 hours, optionally preceded by an extraction step with refluxing solvents, but always for short time in order to prevent the lycopene degradation.
U.S. Pat. No. 6,235,315 discloses stable, pulverulent lycopene formulations characterised in that lycopene has a certain degree of crystallinity and the lowest possible degree of isomerization.
WO 03/090554 discloses concentrated tomato derivatives having high content of lycopene and pre-determined viscosity and sugar content. The process is physical and no solvent is used. Heating for 1-6 minutes II is carried out on round tomatoes in order to make the pulp separation easier.
Mayer-Miebach at al., “Thermal processing of carrots: lycopene stability and isomerisation with regard to antioxidant potential” Food Research International, Elsevier Applied Science, Barking, GB, vol. 38, no. 8-9, October 2005, pages 1103-1108, study the isomerisation of lycopene in freeze-dried carrots in function of temperature. The Authors conclude that only the all-trans isomer is stable to prolonged heating, resulting in a decrease of cis-isomers.
As a matter of fact, therefore, the prior art does not provide isomerisation processes of lycopene comprising a prolonged heating in organic solvents allowing to obtain a product having high bioavailability and stable isomeric composition.